Re: [bug, 5.2.16] kswapd/compaction null pointer crash [was Re: xfs_inode not reclaimed/memory leak on 5.2.16]

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On Mon, Oct 07, 2019 at 03:56:41PM +0200, Vlastimil Babka wrote:
> On 10/7/19 3:28 PM, Vlastimil Babka wrote:
> > On 10/1/19 9:40 PM, Florian Weimer wrote:
> >> * Vlastimil Babka:
> >>
> >>
> >> See below.  I don't have debuginfo for this build, and the binary does
> >> not reproduce for some reason.  Due to the heavy inlining, it might be
> >> quite hard to figure out what's going on.
> > 
> > Thanks, but I'm still not able to "decompile" that in my head.
> 
> While staring at the code, I think I found two probably unrelated bugs.
> One is that pfn and page might be desynced when zone starts in the middle
> of pageblock, as the max() is only applied to page and not pfn. But that
> only effectively affects the later pfn_valid_within() checks, which should
> be always true on x86.
> 
> The second is that "end of pageblock online and valid" should refer to
> the last pfn of pageblock, not first pfn of next pageblocks. Otherwise we
> might return false needlessly. Mel, what do you think?
> 

I think you are correct in both cases. It's perfectly possible I would
not have observed a problem in testing if zones were aligned which I
think is generally the case on my test machines.

-- 
Mel Gorman
SUSE Labs




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